1. Field of the Invention
The present invention relates to an addressing method for X-Y matrix devices comprising liquid crystal cells, intrinsic electroluminescent cells, or the like.
2. Description of the Prior Art
A prior art method for addressing X-Y matrix cells will be described in connection with a two-tone display device comprising liquid crystal cells, the apparent birefringence of which is controlled by an externally applied voltage. According to the prior art method, the frequency f (1/T Hz) of the voltage applied is determined to be higher than the reciprocal of the response of the liquid crystal molecule so that the apparent birefringence of the liquid crystal cell depends on the effective value of the voltage applied.
This two-tone matrix device comprises N numbers of Y electrodes, Y.sub.1 to Y.sub.N, in one dimension of the matrix, and M numbers of X electrodes, X.sub.1 to X.sub.M, in the other dimension. Scanning voltages e.sub.Y1, e.sub.Y2, . . . ,e.sub.YN are applied to the Y electrodes Y.sub.1, Y.sub.2, . . . , Y.sub.N respectively at a cycle T, while, signal voltages e.sub.x1, e.sub.x2, . . . , e.sub.XM are applied to the X electrodes X.sub.1, X.sub.2, . . . , X.sub.M respectively at the same cycle T. The scanning voltage e.sub.Yj and the signal voltage e.sub.Xi will assume waveforms as shown in FIG. 1 (a) if these voltages are given as a pulse train comprising N numbers of time slots over the period of a cycle T. In each time slot which corresponds to the period T/N, the scanning voltages e.sub.Y1, e.sub.Y2, . . . sequentially assume a "1" state, i.e., a - V.sub.1 level in FIG. 1(a), and e.sub.Yk (where K.noteq. j; k = 1,2, . . . , N) assumes a "0" state, i.e., a V.sub.2 level in FIG. 1 (a) whenever e.sub.Yj is in the "1" state. In this manner the Y electrodes are scanned. While, in the j-th time slot, the signal pulse voltage e.sub.Xi applied to the electrode X.sub.i which corresponds to the i-th cell assumes a "1" state, i.e., a V.sub.4 level in FIG. 1 (a), whereby the point selected among M number of cells P.sub.ij (where i = 1,2, . . . , M) which corresponds to the Y.sub.j electrode on the X-Y matrix is determined. The signal voltage e.sub.Xi in the j-th time slot which corresponds to the unselected cells P.sub.ij assumes a "0" state, i.e., a V.sub.3 level in FIG. 1 (a). Thus the voltage e.sub.Xi - e.sub.Yj is applied to the X-Y matrix cell P.sub.ij, and the pulse pattern in each time slot of the signal voltage e.sub.Xi determines a matrix cell to be selected, and the selected cell is scanned by the scanning voltage e.sub.Yj whereby the pattern designated by the signal pattern is displayed. FIG. 2 shows a pattern displayed on the matrix in response to the signal voltages e.sub.X1, e.sub.X2, . . . , e.sub.X5 shown in FIG. 1 (a).
In the prior art method, as described, an arbitrary number (0 to N) of "1" pulses are generated in N numbers of the time slots of the signal voltage e.sub.Xi (where i = 1,2, . . . , M) whereby the desired cells on the X-Y matrix are selected for display. Under this mode of signal voltage, however, the voltage e.sub.Xi -e.sub.Hj which is applied to the cell P.sub.ij necessarily assumes various waveform modes.
FIG. 1 (b) shows waveforms of the voltage e.sub.Xi - e.sub.Yj in relation to FIG. 1(a). Generally, the X-Y matrix cell is not an ideal element in view of the rise characteristics (or threshold voltage) and it is limited in response to the voltage applied, since such response depends on the frequency of the voltage applied. For these reasons the cell P.sub.ij offers unnecessary responses when the voltage e.sub.Xi - e.sub.Yj is applied in various waveforms. Furthermore, it is likely that a voltage such as e.sub.X3 - e.sub.Y2 or e.sub.X2 - e.sub.X6 in FIG. 1(b) is applied to an unselected point Pu to cause an unselected cell to become responsive. This necessarily determines the upper limit of the response contrast U. Generally, when the value of N is large, the upper limit of the contrast is low. Thus, in the prior art method for an X-Y matrix device comprising liquid crystal cells driven in response to the effective value of the voltage applied, the intensity of the light transmitted through the device is variable. (In some cases this problem may be solved by the use of a matrix addressing method capable of maintaining uniform the influence of cross-talk upon the picture quality.) Furthermore, according to the prior art, the ratio between light intensities at a selected point and at an unselected point, that is, the contrast, cannot be made high enough, which makes it impossible to realize satisfactory response of matrix cells.